Evolution of NITrogen BUFFERing capacity of land water interfaces along hydrosystems of different age (NITBUFFER)

河漫滩、河岸带和河道内带是河流生态系统中能量和物质转移的重要调节器。更具体地说，河流景观中的陆地-水生界面，例如河岸森林或草甸、湿地、砾石坝，在那里发生物理沉积和生物活动;充当生态地球化学热点，特别是氮循环。这些界面也代表了功能保留区，即控制和维持河流水质的缓冲区（Haycock等人，1997年）（Sabater等人，2003年）。经验证据表明，水-基质界面面积（即水-沉积物或湿地-旱地接触长度）与河流生态系统中氮的截留和吸收效率呈正相关。然而，努力量化的重要性，陆地-水界面的氮循环和缓冲能力，在流域流域在很大程度上是不成功的，因为; ㈠在现场研究这些界面的尺度与在更大尺度上推断其能力之间的差异，㈡人类活动导致世界大部分地区河流生态系统破碎化和生境破坏，破坏了这些河流生态系统的结构和功能，因此很难准确地解释这些陆地-水界面的作用。然而，河岸带现在被公认为一种工具，既可以保护河流质量免受扩散污染，又可以促进河流栖息地的再生。然而，我们缺乏一个基本的了解，这种恢复对这些陆地-水界面的氮缓冲能力的后果。此外，河流恢复的基础上恢复河岸带的轨迹没有完全理解，主要是因为我们不知道的自然机制，水文地貌和微生物过程相互作用和这些相互作用的时间框架，以实现氮的缓冲能力。拟议的研究的总体目标是使用不同的年龄和复杂性，在过去250年的冰川消融后，在阿拉斯加州东南部的冰川湾流域作为一个自然的海洋性气候下的原位实验室，分析水文地貌的发展和微生物过程控制氮缓冲能力在水文系统的陆地-水界面的共同演变。这项研究将提供第一个洞察到自然的时间框架的陆地水界面的形成和发展，其后果对氮调节流集水区。冰川湾海洋性气候下的原始水文系统的选择是适当的，因为：i）存在一个有据可查的时间序列，无论是在植被和河流动物群的演替方面，ii）空间-时间的战略可以用来量化陆地-水结构和功能的变化率; iii）地球化学示踪剂不受这种原始环境中过去和现在人类遗产的影响，和iv）相似大小（约10平方公里）的流域的选择，允许确定景观结构和安排的重要性，对N通量要确定。这个天然的原位实验室允许制定和测试有关的陆地-水界面的形成和氮缓冲能力的发展的假设。调节陆地-水界面氮循环的微生物过程的原位速率测量、有机质特征和浓度以及地球化学指标，将为氮陆地-水缓冲区的演变速率提供有价值的数据。这些数据对于了解冰川消退对温室气体排放（N2 O，CO2，CH 4）的影响以及氮缓冲能力随时间推移而发展的机制至关重要。

Floodplain, riparian and in-stream zones are key regulators of energy and matter transfer in river ecosystems. More specifically, terrestrial-aquatic interfaces in riverine landscapes, e.g. riparian forest or meadow, wetlands, gravel bars, where physical sedimentation and biological activities occur; act as biogeochemical hot spots, particularly for nitrogen cycling. These interfaces also represent functional retention areas, i.e. buffer zones (Haycock et al. 1997) which control and maintain river water quality (Sabater et al. 2003). Empirical evidence has shown that the area of water-substrate interface (i.e. water-sediment or wetland-upland length of contact) is positively correlated to the efficiency of nitrogen retention and uptake in river ecosystems. Nevertheless, efforts to quantify the importance of land-water interfaces on nitrogen cycling and their buffering capacity in drainage basins have largely been unsuccessful due to; i) the discrepancy between the scales at which these interfaces have been studied in situ and the extrapolation of their capabilities at larger scales, and ii) anthropogenic activities which have led to river ecosystem fragmentation and habitat destruction in most parts of the world, disrupting the structure and function of these lotic ecosystems, such that it is difficult to accurately decipher the role of these land-water interfaces. However, riparian zones are now well recognised as a tool to allow both protection of river quality against diffuse pollution and to promote the regeneration of stream habitats. Yet, we lack a fundamental understanding of the consequences of this restoration on the nitrogen buffering capacities of these land water interfaces. Moreover the trajectory of stream restoration based on the rehabilitation of riparian zones is not fully understood, mostly because we do not know the natural mechanisms by which hydrogeomorphological and microbial processes interact and the timeframe of these interactions to achieve nitrogen buffering capacities. The overall goal of the proposed research is to use watersheds of different ages and complexity that have developed during the last 250 years following deglaciation in Glacier Bay, southeast Alaska as a natural in-situ laboratory under maritime climate to analyse the co-evolution of hydrogeomorphic development and microbial processes controlling nitrogen buffering capacity in hydrosystems' land water interfaces. This research will provide the first insights into the natural timeframe of land water interface formation and development, and their consequences on nitrogen regulation in stream catchments. The choice of pristine hydrosystems under Maritime climate in Glacier Bay is appropriate due to: i) the existence of a well documented chronosequence, both in terms of vegetation and stream fauna successions; ii) space-for-time strategies can be used to quantify rates of change of land water structure and functions; iii) geochemical tracers are not influenced by past and present human legacy in this pristine context, and iv) the selection of drainage basins of similar size (ca 10 km2) permits to determine the importance of landscape structure and arrangement on N fluxes to be determined. This natural in-situ laboratory allows the formulation and testing of hypotheses related to the formation of the land water interface and the development of their nitrogen buffering capacity. In situ rate measurements of microbial processes regulating nitrogen cycles in land water interfaces, and organic matter character and concentration, together with geochemical indicators, will provide valuable data on the rate of evolution of nitrogen land water buffer zones. These data are essential for understanding the consequences of deglaciation on greenhouse gas emissions (N2O, CO2, CH4) and the mechanisms by which nitrogen buffering capacity develop over time.